As various new materials have been developed together with scientific technology development, footwear has been rapidly developed ever since a human can walk, so that nowadays, the footwear for various usages suitable for diverse activities, such as walking, climbing, physical correction, specific sports, or the like, have been made.
Especially the footwear for exercise, as the importance of health has been in the spotlight, has made rapid progress, and footwear having new materials and structures have been also continuously developed. Therefore, considering an aspect of physical health, the priority to be solved is better air permeability and cushioning of the footwear.
In order to achieve a fundamental object of surrounding and protecting the foot and allowing a human to act, all kinds of footwear rather than slippers have a formation that their inner surfaces are almost covered up except for a certain upper part through which a human can put on and off the footwear. Therefore, the air permeability aspect of the footwear is basically inevitable due to a characteristic of the footwear. However, various materials having superior air permeability and diverse air permeable structures suitable for footwear have been developed, so that an air permeability problem has been gradually improved.
More important in the physical health aspect than air permeability is cushioning. If the cushioning of the footwear is not good, not only does a human easily feel foot fatigue, but also it may have bad influence on the body because shock caused by contact between the footwear outsole and the ground is transferred to the brain through the spine. Therefore, the footwear should have sufficient cushioning.
The part to which the cushioning is applied is the footwear outsole, of which the problem is considerably solved through the development of the various materials having superior shock absorption. However, it cannot solve all problems of the cushioning only by means of the materials having superior cushioning.
That is, a conventional outsole of footwear is almost shaped like a plane. Therefore, the conventional footwear outsole not only cannot totally relieve shock on the sole of the foot because the footwear outsole is not in close contact with the sole of a foot having big and small curves, specifically, the arch of the foot, but also occurs a problem of making the sole of the foot flat when wearing the footwear for a long time period.
Further, if the footwear cannot stably support the arch of a central part of a human body, and make the arch to be in contact with the footwear outsole, the center of the foot is out of the center so that the pelvis gets twisted and serious problems may occur in the musculoskeletal system.
Therefore, in order to improve the cushioning while more stably supporting the arch of the sole of the foot, footwear having a convex part upwardly protruding from an upper surface of the outsole has developed for being in contact with the arched part.
As described above, the convex part being in contact with the arch advantageously relieves shock transferred to the sole of the foot, specifically, the arch, when walking, so as to reduce foot fatigue. However, a convex shape of the convex part is uniformly mass-produced so as to form a standardized uniform structure, so that a case may occur where the arch of the sole of the foot is not well fitted to the convex part, depending on the person. Therefore, there is a disadvantage in that, as an occasion demands, the knoll rather gives bigger pressure on the arch, or it cannot properly support the arch.
Then, if the convex part cannot closely contact and support the arch, a feeling of foot fatigue is of course increased, and especially, if a user walks for long hours or is flat-footed, the convex part cannot stably support the arch. Therefore, a need for a footwear outsole capable of properly supporting the arch depending on different foot shapes has been on the rise.
Further, shock according to the contact between the ground and the footwear outsole is transferred to the brain through a rear part of the lower surface of the outsole, the heel of the foot, and the spine, so that the development of the structure that can relieve shock of the footwear outsole is also required.